The present invention relates to a method for decoding a suppressed-carrier modulated signal in the presence of a pilot tone, particularly for frequency modulation, and to an apparatus for implementing it.
In conventional signal transmission methods a signal is broadcast by means of suppressed-carrier amplitude-modulated carriers in the presence of a reference tone, known as pilot tone, whose frequency is half that of the signal to be broadcast and whose amplitude is variable.
Demodulation of the signal upon reception occurs by reconstructing the carrier by means of a phase-locking oscillation circuit (PLL) which uses the pilot tone as a reference for locking.
This method is widely used in frequency-modulation (FM) radio broadcasts for stereo signals.
A drawback of the above-described method resides in the fact that although it is suitable for analog implementations, it is poorly suited to digital circuits, since it is impossible to produce digital PLLs.
Moreover, the phase precision of the reconstructed carrier is always affected by an unpredictable error, which can be reduced to very small values in high-level and high-cost equipment.
Finally, the analog implementation requires a large number of components which require calibrations, with the consequent problems in terms of cost, stability and quality in general.